The present invention relates to a system and method for signaling between a plurality of devices over a noisy power line and particularly relates to innovative method and a system for high speed signals using a distinct modulating scheme over direct current (DC) power lines and multiple frequency channels, and an innovative device to test communication over DC power lines with adjustable conditions.
More and more tasks today require complete or partial computer control. Particularly in transportation, multiple computers, sensors and actuators are an integral part of many machines. Cars, boats, aircraft, and trains use computers to make the engine run efficiently, and to run climate control systems, radios, communication equipment, alarm systems, navigation equipment and on board radar. Traditionally, data were passed between computers, sensors and actuators through dedicated wires and data buses. Large numbers of dedicated communication wires greatly complicates the production and maintenance of vehicles.
Recently there has developed interest in reducing the need for dedicated communication wires by using existing electric power lines as a communication media. Interest has mostly been directed toward using AC power lines to promote communication between appliances, computers and equipment within and between buildings.
Less attention has been directed toward DC power lines, which are used in vehicles. Using DC power lines for communication reduces the space and weight dedicated to communication wiring in vehicles including, for example, automobiles, trains, aircraft and satellites. Reducing the size and weight of vehicles reduces cost of production and increases efficiency and performance.
Maryanka (U.S. Pat. No. 5,727,025) teaches high-speed transmission of data over DC power lines with error control by means of channel coding and modulation. DC power-line communication may be over a single channel or multiple channels as presented in EAEC sixth European ITS conference in Cernobbio Italy on 2–4 Jul. 1997 by Mr. Aldo Romaro et al. “Super Integration In Automotive Electronics” page 1105.
When a plurality of devices communicates over a shared medium such as a DC power line, there is a need to coordinate sharing of the media. Therefore, in order to facilitate communication over noisy media such as DC power lines there must an efficient signaling method. Signaling is used for sending predetermined messages; for example, to turn on or off a particular appliance. Signaling is also used for sending of supervisory information for maintaining communication on a channel. For example: a transmitter uses signaling to instruct a receiver to prepare for a new transmission; a transmitter uses signaling to indicate intention to use a channel in order to prevent other transmitters from interfering with communication on the channel; a receiver uses signaling to inform a transmitter of a reception error; a receiver uses signaling to inform a transmitter of a speed limitation, a receiver uses signaling to inform a transmitter of a congestion condition wherein the receiver cannot receive (for example: due to a full input buffer or due to an incoming message on a separate channel), a receiver uses signaling to send to a transmitter a request to retransmit.
Signaling is commonly used for collision detection and collision resolution (detection of potential interference between transmissions by multiple devices on a channel and coordination of communication to avoid the interference). For efficient collision detection and resolution on a noisy channel, it is necessary to have a signaling method by which competing transmitting devices can quickly signal their intention to use the channel preventing other transmitters from accessing the channel.
DC power lines are considered typically as very noisy communication channels with high level impulse noises, causing communication errors over a wide range of frequencies. In addition, part of the frequencies available for communication may be blocked for long period of time as a result of Electro Magnetic Interference (EMI) or strong attenuation resulting from inter-symbol interference, fading and standing waves. The combination of wide band short-term impulse noise and long time period narrow band interference places stringent demands on signaling. Specifically, the high probability of blocked channels and the large number of communication errors over DC power-lines results in an increased burden of coordination and an increased number of signals. On a noisy channel, signals must be resistant to frequency notch and blocking by noise.
Communication can be for the purpose of transferring arbitrary data or for the purpose of sending one of a predetermined set of messages. Errors cannot be readily detected or corrected in arbitrary data. Therefore, arbitrary data is generally transmitted via symbol codes that have high resistance to random errors. Resistance to errors in symbol codes is achieved by lengthening the symbol transmission period. Lengthening the symbol transmission period slows communication.
Signaling is used for sending a message taken from a predetermined limited set of potential messages. A predetermined finite domain of signals corresponds to the predetermined finite set of messages. When a signal is corrupted, the corrupted signal will seldom correspond to a signal in the domain of potential signals. Therefore, an error is easily recognized. When there is an error, the original intended signal can be retrieved by finding the legitimate signal most similar to the received signal. Thus, signals are inherently resistant to changing the meaning (aliasing). Therefore, the use in signaling of lengthened symbol codes developed for arbitrary data communication implies redundant error protection. Redundant error protection is inefficient and unnecessarily slows signaling.
VanderMey et al. (U.S. Pat. No. 6,034,988) teach a spread spectrum apparatus and method for network RF data communications having extended communication channels. The spectrum spreading method of VanderMey '988 is frequency hopping across a plurality of channels. Frequency hopping allows communication over noisy media. In order to permit simultaneous data hopping and carrier sensing multiple access—collision detection (CSMA-CD) VanderMey '988 requires a means of fast signaling of a free channel. According to VanderMey '988 fast signaling is to be achieved by a RF signal within one sub-symbol of a data packet. However, nowhere does VanderMey '988 disclose a one sub-symbol signaling method. VanderMey does reveal a signaling method by a code of multiple symbols. Because each frequency hop must wait until a signal can be detected on a new channel, signal detection by a code of multiple symbols significantly slows communication in the VanderMey '988 method.
Jaffe et al. (U.S. Pat. No. 5,485,147) teach a method and apparatus for scheduling access to a CSMA communication medium. According to the method of Jaffe et al. '147 signaling is over a dedicated channel that is not available for arbitrary data communication. The additional channel increases network cost because the additional channel requires extra hardware for each component of the network and requires extra bandwidth.
Gold et al. (U.S. Pat. No. 5,488,631) teach a wireless direct-sequence spread spectrum TDMA communications system. The patent of Gold et al. '631 discloses a physical layer method for communication including signaling. The signaling method of Gold et al. '631 is direct sequence spread spectrum communication (DSSS). DSSS was developed for arbitrary data communication. As such DSSS does not take advantage of the limited domain of signals. Thus signaling requests according to Gold et al. '631 require more communication resources than optimized signaling. Furthermore, DSSS requires the generation of complex pseudo-noise functions and modulation and demodulation of signals by means of the pseudo-noise functions. Generation and modulation with pseudo-noise functions increases the complication and expense of each transmitter and receiver on the network of Gold et al. '631. The system of Gold et al. '631 is well suited for a DSSS network wherein transmitters and receivers are necessarily equipped with pseudo-random code generators and modulators and wherein messages are long. But in a network where messages are short and devices are relatively simple, the method of Gold et al. '631 requires dedication of an unnecessarily large quantity of resources to CSMA-CD and signaling.
Thompson (U.S. Pat. No. 5,726,976) teaches a congestion sense controlled access for a star configured network. According to Thompson '976 the communication rate can be increased over a carrier sense network (with emphasis on Ethernet networks) by reduction of the packet length. Thompson '976 further reveals a method for duplex communication over star configured network. In order to achieve full duplex, Thompson '976 requires in-band signaling. While one goal of Thompson '976 is to reduce the communication packet length the revealed method of in-band signaling requires block encoding including extra signaling bits in the transmitted data. Block encoding increases the packet length and decreases communication efficiency.
Communication devices are often required to function under a variety of conditions. For example a particular set of devices may be used in different vehicles and under different operating conditions. When developing or trouble shooting a communication device it is unfeasible and prohibitively expensive to install and test a device in every possible configuration and under all possible conditions. Therefore testing is done using a testing apparatus.
Prior art systems for testing a communication device require installation into a particular environment or do not allow for varying the testing conditions without permanent modification of the testing apparatus. For example, Wieczorek, et al. (U.S. Pat. No. 5,703,479) reveal a system for loopback testing of electronic equipment. But the method of Wieczorek et al. '479 makes no allowance for changing conditions under which the equipment operates. Fieramosca, et al. (U.S. Pat. No. 5,950,149) reveal a “Method for testing vehicle electrical system during manufacturing”. The method of Fieramosca et al. '149 requires testing the electrical system after installation in a car and cannot make account for individual differences between cars or changes in conditions (for example, as a car ages). Yoshida, et al. (U.S. Pat. No. 6,205,202) reveal a method of testing home communications lines. Yoshida '202 fails to consider the importance of differing performance under particular environmental conditions.
There is thus a widely recognized need for, and it would be highly advantageous to have a signaling system and method to allow fast signaling and CSMA-CR over noisy communication circuits. Further, there is a widely recognized need for, and it would be highly desirable to have a device to facilitate testing of communication installed in different pieces of equipment or functioning under varying environmental conditions.
Definitions
For the sake of the present patent the following definitions will be used:
a collision is an intent of a plurality of transmitters to transmit during a particular common time period on a specific channel;
a collision resolution is a decision not to transmit during the particular time period on the specific channel in all but one transmitter involved in a collision.
a channel is a defined part of communication carrier through which a limited quantity of information is transmitted; for example, a channel may include a frequency band from a frequency range in a radio signal or in an optical signal, and a wire from a group of wires;
a communication carrier is a vehicle by which a message may be sent; electromagnetic waves, sound or ultra-sonic vibrations are common examples of communication carriers;
a communication medium is a physical vessel for conveying a communication carrier; examples of media include but are not limited to a wire, an electromagnetic field, a conduit, and an optical fiber;
a device is a member of communication network that may include components to serve any function and is configured to send a signal, receive a signal or both transmit and receive a signal.